1. Field of the Invention
The present invention relates to a system that uses gases in a microprocess for fabricating semiconductor devices. More specifically, the present invention relates to a processing system of a chemical reaction type, typically, a low-pressure CVD system, and an evacuating system and a trapping device which can be used in combination with a processing system of this kind.
2. Description of the Related Art
Multilevel wiring structures have been used generally in recent years. The progressive increase in device density requires reduction in size of contact holes for connecting metal wiring lines in different wiring layers. Consequently, the aspect ratio (=(Depth of hole)/(Width of hole)) of contact holes increases accordingly. The enhancement of the operating speed of the individual component semiconductor elements and devices of chips requires the use of materials having low resistance for forming wiring layers and filling up contact holes.
To meet demand for miniaturization and resistance reduction, the use of copper as a material for forming metal wiring lines instead of aluminum which has been generally used for forming metal wiring lines and techniques for forming copper films by a CVD process (chemical vapor deposition process) have been studied.
Generally, organic copper compounds are used for forming a copper film by a CVD process. Cu(I)hfacTMVS is a notable material. In the term Cu(I)hfacTMVS, hfac is an abbreviation for hexafluoroacetylacetonate, the term TMVS is an abbreviation for trimethylvinyl silane, and Cu(I) indicates univalent copper. In the following description, the terms Cu(II) and Cu(0) indicate bivalent copper and metallic copper, respectively. Cu(I)hfacTMVS is a low-viscosity liquid at an ordinary temperature and has a moderate vapor pressure of 1 torr at 60° C. Therefore, Cu(I)hfacTMVS can be relatively easily gasified into a source gas by a system including a liquid supply system and a gasifier and the source gas can be supplied into a reaction chamber or a processing chamber. Since Cu(I)hfacTMVS is subject to decomposition at temperatures not lower than 70° C., a copper film can be formed on a substrate at a deposition rate that does not cause any problem in the process by using Cu(I)hfacTMVS.
Other possible organic copper compounds are β-diketonate compounds, such as Cu(II)(hfac)2, and cyclopentadienyl compounds, such as CpCuTEP. However, since those copper compounds are solid at an ordinary temperature, those copper compounds are difficult to supply in gases into a processing chamber. A high temperature not lower then 380° C. is necessary for decomposing Cu(II)(hfac)2. CpCuTEP has a very low vapor pressure of 0.01 torr at 80° C. and hence it is difficult to supply CpCuTEP at a sufficiently high partial pressure to the processing chamber when depositing a film.
Cu(I)hfacTMVS. as compared with other organic copper compounds, can be easily gasified and supplied into a processing chamber by using a system including a liquid supply system and a gasifier and a film can be deposited at a relatively low temperature by using Cu(I)hfacTMVS.
Generally, copper films are deposited by a low-pressure CVD process. A CVD processing chamber is evacuated to a predetermined pressure, and unused source gases and reaction byproduct gases are discharged from the processing chamber by a vacuum pump. Since it is possible that oil is diffused into the processing chamber when a wet vacuum pump, such as an oil-sealed rotary vacuum pump, is used, a dry vacuum pump free from such a problem is used in most cases.
The condensation temperature and the decomposition temperature of Cu(I)hfacTMVS gas are close to each other. This characteristic of Cu(I)hfacTMVS is a problem with the evacuating system for a low-pressure CVD process.
Unused Cu(I)hfacTMVS sucked from the processing chamber condenses in the vacuum pump if the temperature in the vacuum pump is low and will cause troubles in rotary components of the vacuum pump and, if things come to the worst, the rotary components may be damaged.
Generally, the interior of the vacuum pump is heated to avoid the condensation of Cu(I)hfacTMVS. It is hardly possible to maintain parts of a complex structure, such as the vacuum pump, uniformly at the same temperature, and the temperatures of different parts of the vacuum pump differ necessarily from each other. The decomposition of Cu(I)hfacTMVS around parts of relatively high temperatures proceeds and it is possible that copper deposits on those parts. If those parts are maintained at a lower temperature to avoid the deposition of copper, Cu(I)hfacTMVS condenses on those parts.
In the low-pressure CVD process using Cu(I)hfacTMVS as a source gas, it is very difficult to suppress the condensation and the decomposition of Cu(I)hfacTMVS simultaneously in the vacuum pump.
In this CVD process, Cu(I)hfacTMVS decomposes into Cu(0) and Cu(II)(hfac)2. Although Cu(0) produced by reaction forms a copper film, the reaction byproduct, Cu(II)(hfac)2 containing 50% of Cu atoms contained in the source gas is disposed of. Thus, the resource utilizing efficiency of the CVD process has been low.